Abstract

Measurements are reported of NH exchange rates of urea, thiourea, acetamide and thioacetamide, using line-shape analysis with natural-abundance ^(15)N NMR spectra. Base-catalyzed NH-proton exchange of thiourea is 30–40 times faster than for urea, while the corresponding acid-catalyzed exchange is 150 times slower. The base-catalyzed proton exchange for thioacetamide is about 1000 times faster than that of acetamide at 25°C, while the corresponding acid-catalyzed exchange is some 260 times slower.